The present invention relates to an information processing device and an optical disk memory for use therewith, and, in particular, relates to a portable and thin type information processing device and an optical disk memory used therein.
Optical disks having a large memory capacity have been broadly used for various applications with development of our information-oriented society. The optical disk memories are classified broadly as reproduction-only type, write-once type, and rewritable type. The reproduction-only type, represented by a compact disk, records information in the form of a recess and a projection on a substrate with such devices as stampers, such that a large quantity of memory medium of inexpensive cost can be supplied. The reproduction-only type optical disk, in other words, the ROM type optical disk, is suitable for use as a memory medium for commercial software, such as game software, picture image processing software, and word processing software, because this memory element can be supplied at an inexpensive cost and in large quantity, and additionally has the ability to maintain a high reliability of the recorded information regardless of heat and external magnetic fields. On the other hand, the write-once type and rewritable type optical disks record information through pit formation, phase change, or magnetization reversal, which is caused by heating recording materials of thin film with laser beam irradiation, and there is an increasing demand for use of such devices as large capacity memory devices for private use, such as document files and picture image files. However, in the above-mentioned reproduction-only type optical memory, a metallic film, such as aluminum or gold, is formed on the substrate to a thickness where the transmitting light almost disappears, due to a high reflectivity of more than 75%. On the other hand, the write-once type and rewritable type optical memories have a requirement to increase their absorptivities to as large an extent as possible for effectively utilizing the heat energy of the irradiated laser beam, with the result that the reflectivity of these devices is as low as about 15 to 30%. Therefore, it has been difficult to use the same optical disk device for both the reproduction-only type disk and the write-once and rewritable type optical disks in common. In addition, a low rank optical disk device designed for the reproduction-only type disk can not read information recorded on the optical disk of the write-once type and rewritable type.
Conventionally, in some write-once type and rewritable type optical disks, a ROM part was formed on a part of the disk, such as through pre-pit formation. However, the ROM part of these disks was provided with basically the same disk structure as that of the write-once and rewritable part so as to maintain the reflectivity constant and hold down production costs. Further, this disk was provided with a film including recording materials. Namely, the optical characteristics of recording materials in the ROM part of the conventional write-once type and rewritable type optical disks was subject to change, such as by temperature, external magnetic fields, and irradiation of the recording beam caused by erroneous operation of the optical disk device, with the possible loss of recorded information and the creation of reproduction error due to such loss of information and reduction of information quality. A ROM type optical disk with which the present invention deals has a film constitution including no recording material, such as provided on a compact disk and a laser disk, and pertains to a reproduction-only type optical disk having a high reliability with regard to recorded information, and is different from the ROM part in the conventional write-once type and rewritable type optical disks.
On the other hand, there has been a demand for a thinner type optical disk medium for use with a lap top computer and a portable optical disk device. Conventionally, an example of a thin, card size optical disk memory is disclosed in JP-A-60-79581 (1985), wherein a disk type optical memory medium is rotatably mounted in a case of credit card size for facilitating handling. Moreover, by emitting a laser beam through a transparent opening portion of the case, the case can serve as a part of a transparent substrate having a thickness of 1.2 mm and a thin optical disk memory is realized. However, even with such a disk type optical memory medium in a card size case, no optical memory medium having compatibility between the reproduction-only type, and the write-once type and rewritable types, and no optical memory system capable of using the same interchangeably have been realized.
As explained above, realization of compatibility between the optical disk devices of the reproduction-only type, and the write-once type and rewritable type was conventionally difficult due to the reflectivity difference of the optical disks. Especially, because the compatibility in a low rank device was not realized, information in a write-once type and rewritable type optical disk could not be reproduced with a reproduction-only type optical disk device.
Further, while an optical disk as an exchangeable memory medium has a large memory capacity, its package is large in comparison with such memory elements as a floppy-disk and an IC card, with the result that its thickness must be reduced if it is to be used as a memory for such devices as a lap top computer and other portable information processing devices.